Directed emitter/sensor for electromagnetic tracking in augmented reality systems

ABSTRACT

A method of operating a head mounted augmented reality display system includes producing an electromagnetic field using an electromagnetic emitter, positioned in a handheld controller and reflecting the electromagnetic field using a first electromagnetic reflector, positioned adjacent to the electromagnetic emitter, to form a modified electromagnetic field. The method also includes reflecting a portion of the modified electromagnetic field using a second electromagnetic reflector positioned in a headset and detecting the reflected portion of the modified electromagnetic field by an electromagnetic sensor positioned adjacent to the second electromagnetic reflector.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is continuation of U.S. patent application Ser. No.17/145,177, filed Jan. 8, 2021, entitled “DIRECTED EMITTER/SENSOR FORELECTROMAGNETIC TRACKING IN AUGMENTED REALITY SYSTEMS,” which is acontinuation of U.S. patent application Ser. No. 16/561,669, filed Sep.5, 2019, U.S. Pat. No. 10,915,164, issued Feb. 9, 2021, entitled“DIRECTED EMITTER/SENSOR FOR ELECTROMAGNETIC TRACKING IN AUGMENTEDREALITY SYSTEMS,” which is a non-provisional of and claims the benefitof priority to U.S. Provisional Patent Application No. 62/727,489, filedSep. 5, 2018, entitled “DIRECTED EMITTER/SENSOR FOR ELECTROMAGNETICTRACKING IN AUGMENTED REALITY SYSTEMS,” the contents of which are herebyincorporated by reference in their entirety for all purposes.

BACKGROUND OF THE INVENTION

Modern computing and display technologies have facilitated thedevelopment of systems for so called “virtual reality” (VR) or“augmented reality” (AR) experiences, wherein digitally reproducedimages or portions thereof are presented to a user in a manner whereinthey seem to be, or may be perceived as, real. A VR scenario typicallyinvolves presentation of digital or virtual image information withouttransparency to other actual real-world visual input; an AR scenariotypically involves presentation of digital or virtual image informationas an augmentation to visualization of the actual real-world around theuser.

Despite the progress made in these display technologies, there is a needin the art for improved methods and systems related to augmented realitysystems, particularly, display systems.

SUMMARY OF THE INVENTION

The present disclosure relates to virtual reality and/or augmentedreality imaging and visualization systems. The present disclosurerelates generally to methods and systems related to electromagnetictracking in virtual reality and/or in augmented reality systems. Moreparticularly, embodiments of the present disclosure provide methods andsystems for directing energy transmitted by an emitter (also referred toas a transmitter) and/or received by a sensor (also referred to as areceiver) to improve performance of localization processes. In someembodiments, a shaped electromagnetic (EM) reflector is utilized tomodify emission patterns generated using an EM emitter/receptionpatterns received by an EM sensor. In some embodiments, unshaped EMpatterns may be prone to distortion, which may affect its ability todetermine position and orientation accurately. In some embodiments, ashaped EM field may minimize distortions and may increase fieldstrength. As a result, field strength in a vicinity of theelectromagnetic sensor is increased. Similarly, the receptive capabilityof the electromagnetic sensor in the direction of the electromagneticemitter is increased. These modifications may result in improvedlocalization information, improved efficiency in power consumption,reduction in EM distortion, as well as reduction in size of theelectromagnetic emitter and/or electromagnetic sensor. The disclosure isapplicable to a variety of applications in computer vision and imagedisplay systems.

According to an embodiment of the present invention, an electromagnetictracking system is provided. The electromagnetic tracking systemincludes a hand held controller including an electromagnetic emitterconfigured to generate an electromagnetic field characterized by anelectromagnetic field pattern and a first electromagnetic reflectorpositioned adjacent the electromagnetic emitter and configured to form amodified electromagnetic field pattern. The electromagnetic trackingsystem also includes a head mounted augmented reality display includingan electromagnetic sensor configured to sense the electromagnetic fieldand a second electromagnetic reflector adjacent to the electromagneticsensor configured to optimally sense electromagnetic field pattern in aregion of interest.

According to a specific embodiment of the present invention, a method ofoperating an electromagnetic tracking system is provided. The methodincludes generating an electromagnetic field using an electromagneticemitter and reflecting the electromagnetic field using a firstelectromagnetic reflector to form a modified electromagnetic fieldpattern. The method also includes reflecting a portion of the modifiedelectromagnetic field pattern using a second electromagnetic reflectorand sensing the reflected portion of the modified electromagnetic fieldpattern using an electromagnetic sensor adjacent the secondelectromagnetic reflector.

Numerous benefits are achieved by way of the present disclosure overconventional techniques. For example, embodiments of the presentdisclosure provide methods and systems that increase electromagneticfield strength in a predetermined manner. Accordingly, systems canachieve desired functionality while reducing transmit power, reducingcomponent size, reducing or avoiding EM distortions, and the like. Theseand other embodiments of the disclosure along with many of itsadvantages and features are described in more detail in conjunction withthe text below and attached figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically illustrates a system diagram of an electromagnetic(EM) tracking system, according to some embodiments.

FIG. 2 is a flowchart describing functioning of an electromagnetictracking system, according to some embodiments.

FIG. 3 schematically illustrates an electromagnetic tracking systemincorporated with an augmented reality (AR) system, according to someembodiments.

FIG. 4 is a flowchart describing functioning of an electromagnetictracking system in the context of an AR device, according to someembodiments.

FIG. 5 is a plan view of an electromagnetic emitter and correspondingelectromagnetic field lines, according to some embodiments

FIG. 6 is a plan view of an electromagnetic emitter incorporating atwo-sided reflector and corresponding electromagnetic field lines,according to some embodiments.

FIG. 7 is a plan view of an electromagnetic emitter incorporating asegmented reflector and corresponding electromagnetic field lines,according to some embodiments.

FIG. 8 is a plan view of an electromagnetic emitter incorporating athree-sided reflector and corresponding electromagnetic field lines,according to some embodiments.

FIG. 9 is a plan view of an electromagnetic emitter incorporating ahemispherical reflector and corresponding electromagnetic field lines,according to some embodiments.

FIG. 10A is a perspective diagram illustrating integration of anelectromagnetic emitter incorporating a three-sided reflector with ahand held controller, according to some embodiments.

FIG. 10B is a perspective diagram illustrating integration of anelectromagnetic sensor incorporating a three-sided reflector with aheadset, according to some embodiments.

FIG. 10C is a perspective diagram illustrating an expanded view of thesensor housing illustrated in FIG. 10B.

FIG. 11 is a simplified flowchart illustrating a method of operating anelectromagnetic tracking system incorporating an integrated reflectoraccording to an embodiment of the present invention.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

In an augmented reality (AR) system, the AR system can be designed to beinteractive with a user. As an example, the user may be provided with ahand held controller, also referred to as a totem, that the user canutilize to interact with the AR system. Accordingly, it is useful to beable to determine the position and orientation (e.g., 6 degrees offreedom (DOF) pose) of the totem with respect to other elements of theAR system, including a head-worn display system, also referred to as aheadset or an AR headset, worn by the user.

One approach to achieve high precision localization may involve the useof an electromagnetic (EM) field for example, emitted by electromagneticfield emitters, coupled with electromagnetic field sensors that arestrategically placed on the user's AR headset, belt pack, and/or otherancillary devices (e.g., totems, haptic devices, gaming instruments,etc.). Electromagnetic tracking systems typically include at least oneelectromagnetic field emitter (referred to generally as “emitter”) andat least one electromagnetic field sensor (referred to generally as“sensor”). The emitter generates an electromagnetic field having a knownspatial (and/or temporal) distribution in an environment of the user ofthe AR headset. The sensor measures the generated electromagnetic fieldsat the locations of the sensor. Based on these measurements andknowledge of the distribution of the generated electromagnetic field, apose (e.g., a position and/or orientation) of the sensor relative to theemitter can be determined. Accordingly, the pose of an object to whichthe sensor and/or the emitter is attached can be determined. That is,the relative position of the sensor and the emitter may be determined.

Referring now to FIG. 1 , an example system diagram of anelectromagnetic tracking system is illustrated. In some embodiments, theelectromagnetic tracking system includes one or more electromagneticfield emitters 102 (referred to generally as “emitter 102”) that isconfigured to emit a known electromagnetic field. As shown in FIG. 1 ,the emitter 102 may be coupled to a power supply 110 (e.g., electriccurrent, batteries, etc.) to provide power to the emitter 102.

In some embodiments, the emitter 102 includes several coils (e.g., atleast three coils positioned perpendicular to each other to producefields in the X, Y and Z directions) that generate electromagneticfields. This electromagnetic field is used to establish a coordinatespace (e.g., an X-Y-Z Cartesian coordinate space). This allows thesystem to map a position of electromagnetic sensors 104 a, 104 b (e.g.,an (X,Y,Z) position) in relation to the known electromagnetic field, anddetermine a position and/or orientation of the electromagnetic sensors104 a, 104 b. In some embodiments, the electromagnetic sensors 104 a,104 b (referred to generally as “sensors” 104) may be attached to one ormore real objects. The sensors 104 may include coils in which currentmay be induced through an electromagnetic field, for example, theelectromagnetic field emitted by the emitter 102. The sensors 104 mayinclude coils or loops (e.g., at least three coils positionedperpendicular to each other) coupled together within a small structuresuch as a cube or other container, that are positioned/oriented tocapture incoming electromagnetic flux from the electromagnetic field,for example the electromagnetic field emitted by the emitter 102, and bycomparing currents induced through these coils, and knowing the relativepositioning and orientation of the coils relative to each other,relative position and orientation of the sensors 104 relative to theemitter 102 may be calculated.

One or more parameters pertaining to a behavior of the coils andinertial measurement unit (“IMU”) components operatively coupled to thesensors 104 may be measured to detect a position and/or orientation ofthe sensors 104 (and the object to which it is attached to) relative toa coordinate system to which the emitter 102 is coupled. In someembodiments, multiple sensors 104 may be used in relation to the emitter102 to detect a position and orientation of each of the sensors 104within the coordinate space. The electromagnetic tracking system mayprovide positions in three directions (e.g., X, Y and Z directions), andfurther in two or three orientation angles. In some embodiments,measurements of the IMU may be compared to the measurements of the coilto determine a position and orientation of the sensors 104. In someembodiments, both electromagnetic (EM) data and IMU data, along withvarious other sources of data, such as cameras, depth sensors, and othersensors, may be combined to determine the position and orientation. Thisinformation may be transmitted (e.g., wireless communication, Bluetooth,etc.) to a controller 106. In some embodiments, pose (or position andorientation) may be reported at a relatively high refresh rate inconventional systems. Conventionally an electromagnetic field emitter iscoupled to a relatively stable and large object, such as a table,operating table, wall, or ceiling, and one or more sensors are coupledto smaller objects, such as medical devices, handheld gaming components,or the like. Alternatively, as described below in reference to FIG. 3 ,various features of the electromagnetic tracking system may be employedto produce a configuration wherein changes or deltas in position and/ororientation between two objects that move in space relative to a morestable global coordinate system may be tracked; in other words, aconfiguration is shown in FIG. 3 wherein a variation of anelectromagnetic tracking system may be utilized to track position andorientation delta (change) between a head-mounted component and ahand-held component, while head pose relative to the global coordinatesystem (say of the room environment local to the user) is determinedotherwise, such as by simultaneous localization and mapping (“SLAM”)techniques using outward-capturing cameras which may be coupled to thehead mounted component of the system.

The controller 106 may control the emitter 102, and may also capturedata from the sensors 104. It should be appreciated that the variouscomponents of the system may be coupled to each other through anyelectro-mechanical or wireless/Bluetooth means. The controller 106 mayalso include data regarding the known electromagnetic field, and thecoordinate space in relation to the electromagnetic field. Thisinformation is then used to detect the position and orientation of thesensors 104 in relation to the coordinate space corresponding to theknown electromagnetic field.

One advantage of electromagnetic tracking systems is that they producehigh resolution, highly repeatable tracking results with minimallatency. Additionally, the electromagnetic tracking system does notnecessarily rely on optical trackers, and sensors/objects not in theuser's line-of-vision may be easily tracked.

It should be appreciated that the strength of the electromagnetic field,v, drops as a cubic function of distance, r, from a coil emitter (e.g.,the emitter 102). Thus, an algorithm may be used based on a distanceaway from the emitter 102. The controller 106 may be configured withsuch algorithms to determine a position and orientation of the sensors104 at varying distances away from the emitter 102. Given the rapiddecline of the strength of the electromagnetic field as the sensors 104move farther away from the emitter 102, best results, in terms ofaccuracy, efficiency and low latency, may be achieved at closerdistances. In typical electromagnetic tracking systems, an emitter ispowered by an electric current (e.g., plug-in power supply) and sensorsare located within a 20 feet radius of the emitter. A shorter radiusbetween the sensors and emitter may be more desirable in manyapplications, including AR applications.

Referring now to FIG. 2 , an example flowchart describing a functioningof an electromagnetic tracking system is briefly described, according tosome embodiments. At 202, a known electromagnetic field is emitted. Insome embodiments, an electromagnetic field emitter may generateelectromagnetic fields. For example, each coil of the electromagneticfield emitter may generate an electromagnetic field in one direction(e.g., X, Y or Z). The electromagnetic fields may be generated with anarbitrary waveform. In some embodiments, the electromagnetic fieldcomponent along each of the axes may oscillate at a slightly differentfrequency from other electromagnetic field components along otherdirections. At 204, a coordinate space corresponding to theelectromagnetic field may optionally be determined. For example, acontroller may automatically determine a coordinate space around theemitter and/or sensors based on the electromagnetic field. In someembodiments, the coordinate space may not be determined at this stage ofthe method. At 206, a behavior of coils at the sensors (which may beattached to a known object) may be detected. For example, a currentinduced at the coils may be calculated. In some embodiments, a rotationof coils, or any other quantifiable behavior may be tracked andmeasured. At 208, this behavior may be used to detect a position ororientation of the sensors and/or a known object (e.g., AR headset whichincludes the sensors) with respect to the emitter, or vice versa. Forexample, the controller 106 may consult a mapping table that correlatesa behavior of the coils at the sensors to various positions ororientations. Based on these calculations, the position in thecoordinate space along with the orientation of the sensors and/oremitters may be determined.

In the context of AR systems, one or more components of theelectromagnetic tracking system may need to be modified to facilitateaccurate tracking of mobile components (e.g., emitter and sensors). Asdescribed above, tracking a head pose of the user and orientation may bedesirable in many AR applications. Accurate determination of the headpose and orientation of the user allows the AR system to display theappropriate/relevant virtual content to the user. For example, thevirtual scene may include a virtual monster hiding behind a realbuilding. Depending on the pose and orientation of the head of the userin relation to the building, the view of the virtual monster may need tobe modified such that a realistic AR experience is provided. Or, aposition and/or orientation of a totem, haptic device or some othermeans of interacting with virtual content may be important in enabling auser to interact with an AR system. For example, in many gamingapplications, the AR system can detect a position and orientation of areal object in relation to virtual content. Or, when displaying avirtual interface, a position of a totem, a hand of a user, a hapticdevice or any other real object configured for interaction with the ARsystem can be known in relation to the displayed virtual interface inorder for the system to understand a command, interaction, and the like.Some localization methods including optical tracking and other methodsmay be plagued with high latency and low resolution problems, whichmakes rendering virtual content challenging in many AR applications.

In some embodiments, the electromagnetic tracking system, discussed inrelation to FIGS. 1 and 2 may be adapted to the AR system to detectposition and orientation of one or more objects in relation to anemitted electromagnetic field. Typical electromagnetic tracking systemstend to have a large and bulky electromagnetic emitters (e.g., 102 inFIG. 1 ), which is problematic for head-mounted AR devices, for example,with a totem. However, smaller electromagnetic emitters (e.g., in themillimeter range) may be used to emit a known electromagnetic field inthe context of the AR system.

Referring now to FIG. 3 , an electromagnetic tracking system may beincorporated with an AR system as shown, with an electromagnetic fieldemitter 302 (referred to generally as “emitter 302”) incorporated aspart of a hand-held controller 306 (referred to generally as “controller306”). The controller 306 can be movable independently relative to an ARheadset 301 (or a belt pack 370). For example, the controller 306 can beheld in a hand of a user, or the controller 306 could be mounted to ahand or arm of the user (e.g., as a ring or bracelet or as part of aglove worn by the user). In some embodiments, the controller 306 may bea totem, for example, to be used in a gaming scenario (e.g., amulti-degree-of-freedom controller) or to provide a rich user experiencein an AR environment or to allow user interaction with an AR system. Insome embodiments, the controller 306 may be a haptic device. In someembodiments, the emitter 302 may be incorporated as part of a belt pack370. The controller 306 may include a battery 310 or other power supplythat powers that emitter 302. It should be appreciated that the emitter302 may also include or be coupled to an IMU 350 component configured toassist in determining positioning and/or orientation of the emitter 302relative to other components. This may be especially advantageous incases where both the emitter 302 and electromagnetic field sensors 304(referred to generally as “sensors 304”) are mobile. Placing the emitter302 in the controller 306 rather than the belt pack 307, as shown in theembodiment of FIG. 3 , helps ensure that the emitter 302 is notcompeting for resources at the belt pack 370, but rather uses its ownbattery source at the controller 306. In some embodiments, the emitter302 can be disposed on the AR headset 301 and the sensors 304 can bedisposed on the controller 306 or belt pack 370. Thus, embodiments ofthe present invention provide implementations in which the controller306 is implemented as a hand-held unit, whereas in other embodiments,the controller is implemented in the AR headset 301, whereas inadditional embodiments, the controller is implemented in an auxiliaryunit, for example, belt pack 307. Moreover, in addition toimplementations in which controller 306 is implemented in a singledevice, the functions of the controller and the attendant physicalcomponents can be distributed across multiple devices, for example,controller 306, AR headset 301, and/or an auxiliary unit such as beltpack 307.

In some embodiments, the sensors 304 may be placed on one or morelocations on the AR headset 301, along with other sensing devices suchas one or more IMUs or additional electromagnetic flux capturing coils308. For example, as shown in FIG. 3 , sensors 304, 308 may be placed onone or both sides of the AR headset 301. Since the sensors 304, 308 maybe engineered to be rather small (and may be less sensitive, in somecases), having multiple sensors 304, 308 may improve efficiency andprecision. In some embodiments, one or more sensors may also be placedon the belt pack 370 or any other part of the user's body. The sensors304, 308 may communicate wirelessly, for example, through Bluetooth, toa computing apparatus that determines a pose and orientation of thesensors 304, 308 (and the AR headset 301 to which it is attached). Insome embodiments, the computing apparatus may reside at the belt pack370. In some embodiments, the computing apparatus may reside at the ARheadset 301, or the controller 306. In some embodiments, the computingapparatus may in turn include a mapping database 330 (e.g., mappingdatabase, cloud resources, passable world model, coordinate space, andthe like) to detect pose, to determine the coordinates of real objectsand/or virtual objects, and may even connect to cloud resources and thepassable world model. The controller 306 is able, in an embodiment, tocontrol timing of electromagnetic emission by the electromagneticemitter and sensing by the electromagnetic sensor such that the positionand orientation of the electromagnetic emitter and the electromagneticsensor are computed based on the field from the modified electromagneticfield pattern. In some embodiments, a position and orientation of theelectromagnetic emitter is computed relative to the electromagneticsensor. In other embodiments, a position and orientation of theelectromagnetic sensor is computed relative to the electromagneticemitter. In some embodiments, a position and orientation of theelectromagnetic emitter and the electromagnetic sensor are computed.

As described above, some electromagnetic emitters may be too bulky forAR devices. Therefore the emitter may be engineered to be compact usingsmaller components (e.g., coils) than traditional systems. However,given that the strength of the electromagnetic field decreases as acubic function of the distance away from the emitter, a shorter radiusbetween the sensors 304 and the emitter 302 (e.g., about 3 to 3.5 ft.)may reduce power consumption when compared to traditional systems suchas the one detailed in FIG. 1 .

In some embodiments, this aspect may either be utilized to prolong thelife of the battery 310 that may power the controller 306 and theemitter 302, in one or more embodiments. In some embodiments, thisaspect may be utilized to reduce the size of the coils generating theelectromagnetic field at the emitter 302. However, in order to get thesame strength of electromagnetic field, the power may be need to beincreased. This allows for a compact emitter 302 that may fit compactlyat the controller 306.

Several other changes may be made when using the electromagnetictracking system for AR devices. Although this pose reporting rate israther good, AR systems may require an even more efficient posereporting rate. To this end, IMU-based pose tracking may (additionallyor alternatively) be used. Advantageously, the IMUs may remain as stableas possible in order to increase an efficiency of the pose detectionprocess. The IMUs may be engineered such that they remain stable up to50-100 milliseconds. It should be appreciated that some embodiments mayutilize an outside pose estimator module (e.g., IMUs may drift overtime) that may enable pose updates to be reported at a rate of 10 to 20Hz. By keeping the IMUs stable at a reasonable rate, the rate of poseupdates may be dramatically decreased to 10 to 20 Hz (as compared tohigher frequencies in traditional systems).

If the electromagnetic tracking system can be run at, for example, a 10%duty cycle (e.g., only pinging for ground truth every 100 milliseconds),the AR system may save power. This may mean that the electromagnetictracking system wakes up every 10 milliseconds out of every 100milliseconds to generate a pose estimate. This may directly translatesto power consumption savings, which may, in turn, affect size, batterylife and cost of the AR device (e.g., the AR headset 301 and/or thecontroller 306).

In some embodiments, this reduction in duty cycle may be strategicallyutilized by providing two controllers 306 (not shown) rather than justone controller 306 as illustrated in FIG. 3 . For example, the user maybe playing a game that requires two controllers 306, and the like. Or,in a multi-user game, two users may have their own controllers 306 toplay the game. When two controllers 306 (e.g., symmetrical controllersfor each hand) are used rather than one, the controllers 306 may operateat offset duty cycles. The same concept may also be applied tocontrollers 306 utilized by two different users playing a multiplayergame.

Referring now to FIG. 4 , an example flowchart describing anelectromagnetic tracking system in the context of AR devices isdescribed. At 402, a portable (e.g., hand-held) controller (e.g., thecontroller 306) emits an electromagnetic field. For example, the emitter302 emits the electromagnetic field. At 404, electromagnetic sensors(placed on headset, belt pack, etc.) detect the electromagnetic field.For example, the sensors 304, 308 detect the electromagnetic field. At406, a pose (e.g., position or orientation) of an AR headset/a belt packis determined based on a behavior of the coils/IMUs at the sensors. Forexample, the AR headset 301/the belt pack 370 determine a pose of the ARheadset 301/the belt pack 370 based on the behavior of the sensors 304and/or the IMUs and coils 308. At 408, the pose information is conveyedto the computing apparatus. For example, the pose information isconveyed to the computing apparatus in the AR headset 301 and/or thebelt pack 370. At 410, optionally, a mapping database may be consultedto correlate real world coordinates (e.g., determined for the pose ofthe headset/belt) with virtual world coordinates. For example, themapping database 330 may be consulted to correlate the real worldcoordinates with the virtual world coordinates. At 412, virtual contentmay be delivered to the AR headset and displayed to the user (e.g., viathe light field displays described herein). For example, the virtualcontent may be delivered to the AR headset 301 and displayed to theuser. It should be appreciated that the flowchart described above is forillustrative purposes only, and should not be read as limiting.

Advantageously, using an electromagnetic tracking system similar to theone outlined in FIG. 3 enables pose tracking (e.g., head position andorientation, position and orientation of totems, and other controllers).This allows the AR system to project virtual content (based at least inpart on the determined pose) with a higher degree of accuracy, and verylow latency when compared to optical tracking techniques. Further, thisallows the AR system to track a user input device (e.g., the controller306) with high accuracy, low power consumption (e.g., by the battery210), low latency, and the like.

FIG. 5 is a plan view of an electromagnetic emitter and correspondingelectromagnetic field lines, according to some embodiments. Asillustrated in FIG. 5 , electromagnetic field lines 520 emitted by anelectromagnetic emitter 510 (referred to generally as “emitter 510”)form closed loops that pass through the interior region of the emitter510 along a x-direction, which is substantially parallel to the lineconnecting the poles created by the emitter 510. As illustrated in FIG.5 , the electromagnetic field generated by the emitter 510 extendsequally in both the positive and negative z-directions.

As described above in relation to FIG. 3 , during use, theelectromagnetic field established by the emitter 510 (e.g., the emitter302 in FIG. 3 ) will be detected at the sensors (e.g., the sensor 304 inFIG. 3 )304 in order to provide the desired localization information.Because the transmitted electromagnetic fields extend away from theemitter 510 in both positive and negative z-directions, energy that isdirected in a direction opposing the direction from the emitter 510 tothe sensors will not be utilized, impairing system efficiency.

In some embodiments, the diagrams of FIGS. 6-9 may be based on finiteelement analyses of time-varying electromagnetic fields. In someembodiment, addition of reflectors of various shapes and configurationsat or near coils of an emitter and/or a sensor may increase intensity ofelectromagnetic lines from the emitter and/or at the sensor in a regionof interest (ROI). The ROI may be where motion in an AR or VR system ismostly active. Although the description relates to emitters, similarreflectors may be applied to sensors to increase reception of sensors inthe ROI. FIG. 6 is a plan view of an electromagnetic emitterincorporating a two-sided reflector and corresponding electromagneticfield lines, according to some embodiments. In FIG. 6 , onlyelectromagnetic field lines lying in the x-z plane are illustrated forthe purpose of clarity, but it will be appreciated by one of skill inthe art that a three-dimensional lobe pattern will be present. Asdiscussed more fully below in relation to FIG. 8 , the designillustrated in FIG. 6 can be extended into three dimensions.

Referring to FIG. 6 , two reflective elements, a first reflectiveelement 620 and a second reflective element 622 have been positionedadjacent the emitter 510, thereby providing an integratedelectromagnetic reflector, also referred to as an integrated reflector.The emitter 510 is oriented such that the electromagnetic field passingthru the coils of the emitter are aligned with the x-axis. The firstreflective element 620 is oriented at a predetermined angle, forexample, an angle of 135°, with respect to the x-axis and the secondreflective element 622 is oriented at a predetermined angle, forexample, an angle of 45°, with respect to the x-axis. In other words,the first reflective element 620 is aligned with a diagonal having aslope of −1 measured in the x-z plane and the second reflective element622 is aligned with a diagonal having a slope of +1 measured in the x-zplane. As illustrated in FIG. 6 , the first reflective element 620 andthe second reflective element 622 are joined at apex 630, positioned ata mid-point of the emitter 510.

The first reflective element 620 and the second reflective element 622are fabricated using materials that are highly conductive at thefrequencies at which the emitter 510 operates (e.g., 27 kHz-40 kHz, forinstance, 35 kHz). In some embodiments, a highly conductive metallicplate, for example, a 2 mm thick copper plate, can be utilized to formthe reflective elements 620, 622. In some embodiments, a substratecoated with a highly conductive material may be employed to utilize themechanical properties of the substrate (e.g., plastic) in conjunctionwith the electrical properties of the conductive material coated ontothe substrate. As will be evident to one of skill in the art, thematerials utilized to fabricate first reflective element 620 and secondreflective element 622 are applicable to other reflective elementsdescribed here as appropriate. One of ordinary skill in the art wouldrecognize many variations, modifications, and alternatives.

Because the first reflective element 620 and the second reflectiveelement 622 reflect the electromagnetic field that would have beenestablished in the negative z-direction, electromagnetic field lines 610form a single lobe oriented along the positive z-direction. As a resultof the electromagnetic energy being present in the single lobe, anelectromagnetic field sensor (e.g., the sensors 304) positioned alongthe positive z-axis with respect to the emitter 510 will detect astronger electromagnetic field at a given distance from the emitter 510,thereby improving system performance.

Moreover, the electromagnetic field lines 610 are characterized byhigher intensity fields for a given lobe width. Referring to FIG. 6 ,the presence of the reflective elements 620 and 622 results incompression of the electromagnetic field lines 610, thereby producing ahigher intensity field. The width of the electromagnetic field line 610characterized by half of a maximum field intensity is defined as a fullwidth half maximum of the electromagnetic field. As illustrated in FIG.6 , for electromagnetic field line 610, which has intensity half of themaximum field intensity, the width is equal to W. Accordingly, the fullwidth half maximum of the lobe pattern illustrated in FIG. 6 , which canbe referred to as a modified electromagnetic field pattern, is W. Thiscan be compared to the electromagnetic field produced by the emitter inthe absence of the first reflective element 620 and the secondreflective element 622. Absent the reflective elements 620 and 622, theelectromagnetic field lines 610 would extend over a large area and becharacterized by a full width half maximum larger than W, whichcorresponds to a weaker intensity field in a ROI 640, as well asunwanted EM energy in the non-ROI areas. Accordingly, whereas atraditional electromagnetic field pattern generated by a traditionalemitter would be characterized by an initial full width half maximumwidth, in some embodiments, utilizing reflective structures such as thereflective elements 620 and 622 will generate a modified electromagneticfield pattern that will be characterized by a modified full width halfmaximum width that is less than the initial full width half maximumwidth. In other words, the electromagnetic field lines in the ROI 640have higher intensity fields. Referring to FIG. 6 , the presence of thereflective elements 620 and 622 results in reflection of electromagneticfield lines in addition to original ones when the reflective elements620 and 622 were not present. This, in effect, produces a modified fieldpattern with an intensity field much higher the original field in theROI 640 without the reflective elements 620 and 622. This can becompared to the electromagnetic field produced by the emitter in theabsence of the reflective elements 620, 622, which was illustrated inFIG. 5 . Absent the reflective elements 620, 622, the electromagneticfield lines 610 would extend over a large area and the intensity of thefield in the ROI 640 would be significantly reduced. Accordingly,whereas a traditional electromagnetic field pattern generated by atraditional emitter as shown in FIG. 5 would distribute its energyfields not only in the ROI 640, but also fields in non-ROI areas asshown in FIG. 5 . Utilizing reflective elements such as the reflectiveelements 620 and 622 will generate a modified electromagnetic fieldpattern that will be concentrated in the ROI 640. In the modifiedpattern, distortions caused by metals in regions where electromagneticlines are minimal would be at a minimum. Thus, the reflective elements620 and 622 shield the coils of the emitter and the coils of the sensorfrom distortions caused by metals on the other side of the reflectiveelements 620 and 622. For such a configuration as shown in FIG. 6 , aswell as those on FIGS. 7-9 , the controller 106 may be capable ofcomputing the positions and orientations based on the modified fieldpattern.

FIG. 7 is a plan view of an electromagnetic emitter incorporating asegmented reflector and corresponding electromagnetic field lines,according to some embodiments. A segmented reflector 720 is placedadjacent one side of the emitter 510. The segmented reflector 720includes a first distal reflective element 722, a central reflectiveelement 724, and a second distal reflective element 726. Because theelements of the segmented reflector 720 reflect the electromagneticfield that would have been established in the negative z-direction,electromagnetic field lines 710 form a single lobe oriented along thepositive z-direction. The dimensions, for example, the length, of thereflective elements 720, 724, 726, as well as the angle between thefirst distal reflective element 722 and the central reflective element724, as well as the angle between the second distal reflective element726 and the central reflective element 724, can be selected to controlthe distribution of the electromagnetic field lines 710.

In some embodiments, the length of the central reflective element 724 isequal to the length of the emitter 510 in the x-direction and the anglesbetween the distal reflective elements 722, 726 and the centralreflective element 724 are both 45°. The length of the distal reflectiveelements 722, 726 can be selected as a function of the length of thecentral reflective element 724. As will be evident to one of skill inthe art, increases in the length of the distal reflective elements 722,726 can result in less electromagnetic field being present in theregions behind the distal reflective elements 722, 726 opposite thecenterline of the electromagnetic field pattern. However, increases inthe length of the distal reflective elements 722, 726 can result inincreased system weight and cost. In a similar manner, the anglesbetween the central reflective element 724 and the pair of distalreflective elements 722, 726 can be varied as appropriate to theparticular application. Thus, although equal angles of 45° areillustrated in FIG. 7 , embodiments are not limited to thisimplementation and configurations with other angles can also beutilized. Moreover, the angles do not have to be equal and can bedifferent. One of ordinary skill in the art would recognize manyvariations, modifications, and alternatives.

FIG. 8 is a plan view of an electromagnetic emitter incorporating athree-sided reflector and corresponding electromagnetic field lines,according to some embodiments. In FIG. 8 , only electromagnetic fieldlines lying in the x-z plane are illustrated for the purpose of clarity,but it will be appreciated by one of skill in the art that athree-dimensional lobe pattern will be present with the center of thelobe extending away from the electromagnetic emitter in a directionorthogonal to the x-axis and at an angle of 45° with respect to the x-zplane.

Referring to FIG. 8 , three reflective elements are illustrated. A firstreflective element 812 and a second reflective element 814 arepositioned adjacent the emitter 510. A third reflective element 816,which lies in the x-z plane, is illustrated by dashed lines. In theembodiment illustrated in FIG. 8 , the three reflective elements 812,814, 816 are orthogonal to each other, forming one half of a cubestructure, with the intersection of the three reflective elementsforming the corner vertex of a cube. The emitter 510 is oriented at 45°with respect to the orientation illustrated in FIG. 6 . Accordingly, theplates of the emitter 510 are oriented at 45° to the x-axis in thisembodiment.

Because the first reflective element 620, the second reflective element622, and the third reflective element 816 reflect the electromagneticfield that would have been established in the negative z-direction andthe positive y-direction, the electromagnetic field lines 810 form asingle lobe oriented out of the plane of the figure along the positivez-direction and the negative y-direction. In some embodiments, thepresence of the reflective elements 812, 814, 816 in the half-cubeconfiguration result in efficiency increases of up to a factor of eightand power consumption reductions by up to a factor of eight.Alternatively, the size of the emitter 510 can be reduced for a givenefficiency/power consumption. Moreover, in some embodiments, the size ofthe emitter 510 is reduced while achieving improved efficiency/powerconsumption performance. One of ordinary skill in the art wouldrecognize many variations, modifications, and alternatives.

FIG. 9 is a plan view of an electromagnetic emitter incorporating ahemispherical reflector and corresponding electromagnetic field lines,according to some embodiments. In FIG. 9 , a portion of a hemisphericalreflector 920 lying in the x-z plane is illustrated as a circular arc.It will be appreciated that rotation of the illustrated circular arcaround the z-axis will define the hemispherical shape of thehemispherical reflector. Because the hemispherical reflector 920reflects the electromagnetic field that would have been established inthe negative z-direction, electromagnetic field lines 910 form a singlelobe oriented along the positive z-direction.

FIG. 10A is a perspective diagram illustrating integration of anelectromagnetic emitter incorporating a three-sided reflector with ahand held controller, according to some embodiments. Referring to FIG.10A, a hand held controller 1000 includes an electromagnetic emitter1010 (referred to generally as “emitter 1010”) that is integrated withthree-sided corner-cube reflector 1020. In this example, the three sidesof the reflector lie in the following planes, respectively: first side1022 in the x-z plane, second side 1024 in the x-y plane, and third side1026 in the y-z plane. Reflection, by the three-sided corner-cubereflector 1020, of the electromagnetic field generated by the emitter1010 results in a center of a three-dimensional lobe pattern produced bythe emitter 1010 being aligned with vector 1030 that is aligned with adirection away from the intersection of the three reflector planes inthe direction of a principal line equidistant to the three axes of thethree-sided corner-cube reflector, where each axis corresponds tointersection of two reflectors. As illustrated in FIG. 10A, vector 1030is directed from the origin of the x-y-z coordinate space along a linedirected to point (1, 1, 1) in the x-y-z coordinate space, whichcorresponds to the center of the three-dimensional lobe pattern. Whensuch a three sided corner-cube reflector is applied to the sensor, itwould allow the sensor to sense most effectively along a principal linewhich would be pointed towards the ROI.

In typical use, the hand held controller 1000 is positioned in front ofa user, with surface 1050 generally orthogonal to a line pointing towardthe head of the user and an AR headset worn by the user. A lineconnecting the surface 1050 and the head of the user, as well as thenormal to the surface 1050, is generally parallel to vector 1030. As aresult, since the enhanced directionality of the electromagnetic fieldgenerated by the emitter 1010 produces stronger fields along the vector1030, stronger fields are produced in the vicinity of the head of theuser and the AR headset worn by the user. Similarly, as described inrelation to FIG. 10B below, the headset can include a sensor with acorresponding three-side corner-cube reflector (or other suitableintegrated reflectors as described herein) configured such that maximumreception would be in the ROI where the emitter is expected to be. As aresult, improved system performance is provided in relation toimplementations that do not utilize reflective elements.

FIG. 10B is a perspective diagram illustrating integration of anelectromagnetic sensor incorporating a three-sided reflector with aheadset, according to some embodiments. As illustrated in FIG. 10B, anAR headset 301 includes a sensor housing 1075 that, in some embodiments,is mounted below the right temple of the AR headset 301. FIG. 10C is aperspective diagram illustrating an expanded view of the sensor housing1075 illustrated in FIG. 10B. The sensor housing 1075 includes anelectromagnetic sensor 1070 (referred to generally as “sensor 1070”)that is integrated with a three-sided corner-cube reflector 1072.Reflection, by the three-sided corner-cube reflector, of theelectromagnetic field received by the sensor 1070, results in a centerof a three-dimensional lobe pattern received by the sensor 1070 beingaligned with a vector 1074 that is oriented along a direction pointingaway from the intersection of the three reflector planes in thedirection of a principal line equidistant to the three axes of thethree-sided corner-cube reflector, where each axis corresponds tointersection of two reflectors. As illustrated in FIG. 10B, the vector1074 is directed from the origin of the x-y-z coordinate space along aline directed to point (1, 1, 1) in the x-y-z coordinate space, whichcorresponds to the center of the three-dimensional lobe pattern. Itshould be noted that the x-y-z coordinate space illustrated in FIG. 10Bdiffers from that illustrated in FIG. 10A for purposes of clarity. Asillustrated in FIG. 10B, by applying three sided corner-cube reflector1072 to the sensor 1070, it allows the sensor 1070 to sense mosteffectively along a principal line which would be pointed towards theemitter.

In typical use, since the hand held controller 1000 illustrated in FIG.10A is positioned in front of and below the head of a user, theelectromagnetic field received from the emitter at the sensor housing1075 will be enhanced by the presence of three sided corner-cubereflector 1072. The position of the three sided corner-cube reflector1072 next to the sensor 1070 results in enhanced directionality of theelectromagnetic field received by the sensor 1070. As a result,increased sensitivity of the sensor along the line connecting the handheld controller 1000 and the AR headset 301 is achieved. Thus, thesensor 1070 has increased sensitivity to electromagnetic fields producedin the vicinity of the hand held controller. As a result, improvedsystem performance is provided in relation to implementations that donot utilize reflective elements.

FIG. 11 is a simplified flowchart illustrating a method of operating anelectromagnetic tracking system incorporating an integrated reflectoraccording to an embodiment of the present invention. The method 1100, inwhich the electromagnetic tracking system incorporates one or moreintegrated electromagnetic reflectors, includes, generating anelectromagnetic field using an electromagnetic emitter (1100). Theelectromagnetic emitter can be disposed in a hand held controller thatis one element of the electromagnetic tracking system, including thehand held controller, an auxiliary unit, which can include a controller,and a head mounted augmented reality display. An integratedelectromagnetic reflector can be utilized with either the emitter and/orthe sensor and can be any of the integrated electromagnetic reflectorsillustrated in FIGS. 6-9 of the present specification.

The method also includes reflecting the electromagnetic field using afirst electromagnetic reflector to form a modified electromagnetic fieldpattern (1112). The first electromagnetic reflector can be positionedadjacent the electromagnetic emitter. The first electromagneticreflector can include reflective elements with various geometricalproperties, including two or more reflector plates, which can be joinedat an apex. In other embodiments, three reflector plates are utilizedand arranged to define a corner vertex of a cube. In an alternativeembodiment, the first electromagnetic reflector is formed as a singlereflector element. As an example, the single reflector element can be asegmented reflector as discussed in relation to and illustrated in FIG.7 or a hemispherical reflector as discussed in relation to andillustrated in FIG. 9 .

The method further includes reflecting a portion of the modifiedelectromagnetic field pattern using a second electromagnetic reflector(1114) and sensing the reflected portion of the modified electromagneticfield pattern using an electromagnetic sensor adjacent the secondelectromagnetic reflector (1116). Utilizing a controller, the method mayfurther include controlling timing of generating the electromagneticfield and sensing the reflected portion of the modified electromagneticfield and digitally computing a position and orientation of theelectromagnetic emitter and the electromagnetic sensor based on themodified electromagnetic field pattern.

It should be appreciated that the specific steps illustrated in FIG. 11provide a particular method of operating an electromagnetic emitterincorporating an integrated reflector according to an embodiment of thepresent invention. Other sequences of steps may also be performedaccording to alternative embodiments. For example, alternativeembodiments of the present invention may perform the steps outlinedabove in a different order. Moreover, the individual steps illustratedin FIG. 11 may include multiple sub-steps that may be performed invarious sequences as appropriate to the individual step. Furthermore,additional steps may be added or removed depending on the particularapplications. One of ordinary skill in the art would recognize manyvariations, modifications, and alternatives.

It is also understood that the examples and embodiments described hereinare for illustrative purposes only and that various modifications orchanges in light thereof will be suggested to persons skilled in the artand are to be included within the spirit and purview of this applicationand scope of the appended claims.

What is claimed is:
 1. A method of operating a head mounted augmentedreality display system, the method comprising: producing anelectromagnetic field using an electromagnetic emitter, positioned in ahandheld controller; reflecting the electromagnetic field using a firstelectromagnetic reflector, positioned adjacent to the electromagneticemitter, to form a modified electromagnetic field; reflecting a portionof the modified electromagnetic field using a second electromagneticreflector positioned in a headset; and detecting the reflected portionof the modified electromagnetic field by an electromagnetic sensorpositioned adjacent to the second electromagnetic reflector.
 2. Themethod of claim 1 wherein the electromagnetic field is characterized byan initial full width half maximum and the modified electromagneticfield is characterized by a modified full width half maximum less thanthe initial full width half maximum.
 3. The method of claim 2 whereinthe modified electromagnetic field is characterized by a higher fieldintensity at a lobe center than the electromagnetic field.
 4. The methodof claim 1 wherein a sensor housing is mounted on a right temple of theheadset.
 5. The method of claim 4 wherein the sensor housing ispositioned such that the second electromagnetic reflector is directed ata region of interest defined by an expected location of a higherintensity lobe of a modified electromagnetic field.
 6. The method ofclaim 1 wherein the first electromagnetic reflector defines a firstcoordinate space and a first corner vertex of a first cube lies at theorigin of the first coordinate space.
 7. The method of claim 6 whereinthe electromagnetic emitter is positioned along a line directed at point(1,1,1) in the first coordinate space.
 8. The method of claim 6 whereinthe modified electromagnetic field has a lobe lying along the linedirected at point (1,1,1) in the first coordinate space.
 9. The methodof claim 1 wherein each of the first electromagnetic reflector and thesecond electromagnetic reflector includes three first reflectiveelements and three second reflective elements, respectively.
 10. Themethod of claim 9 wherein the three second reflective elements define aquadrant of a second coordinate space in which the electromagneticemitter is positioned.
 11. The method of claim 1 wherein the secondelectromagnetic reflector defines a second coordinate space and a secondcorner vertex of a second cube lies at the origin of the secondcoordinate space.
 12. The method of claim 1, further comprising using acontroller to control timing of electromagnetic emission and sensing anddigitally compute a position and orientation of the electromagneticemitter and the electromagnetic sensor based on the modifiedelectromagnetic field.